1. Field of the Invention
The present invention relates to a beam scanning type laser marking method and apparatus for marking patterns such as characters on an processing object by scanning the same with a continuous wave (CW) Q-switch pulse laser beam, and moreover to a mask to be applied to such beam scanning type laser marking apparatus.
2. Description of the Related Art
A conventional laser marking method is disclosed in the Japanese Patent Laid-Open No. HEI 2-165881. The method therein is the so-called a mask transmitting type laser marking method. In this method, a mask on which a pattern to be marked such as characters are previously depicted is irradiated with a pulse excitation laser beam. The laser beam having transmitted through the mask is focused on the surface of processing object, that is, on the marking surface. The focused laser beam prints the pattern depicted on the mask to the processing object.
In this mask transmitting type laser marking method, kinds of patterns to be depicted on the mask is limited. Moreover, a mask must be newly generated for every change
Meanwhile, a beam scanning type laser marking apparatus, which is different from the mask transmitting type laser marking apparatus, is disclosed in the Japanese Patents Laid-Open Nos. SHO 59-45091 and 60-221721. In this apparatus, a laser beam obtained by the CW Q-switch pulse oscillation is focused on the marking surface of an processing object. The desired characters or signs are marked on the processing object by making the scanning the surface thereof with the laser beam focused through the use of a scanner mirror.
This beam scanning type laser marking apparatus is not required to use a mask on which the desired pattern is stationarily depicted and moreover to provide a liquid crystal mask and a driving device thereof. Therefore, this apparatus has reasonably reduced the apparatus cost and running cost thereof in comparison with the mask transmitting type laser marking apparatus explained above.
In this beam scanning type laser marking apparatus, an energy density of laser beam for irradiating the surface of processing object is intensified because the laser beam is focused on the marking surface. As a result, substances at the region irradiated with the laser beam is momentarily vaporized and the processing depth of the marking line reaches about 50 to 100 .mu.m. Accordingly, contour of the pattern marked on the processing object becomes ambiguous and the pattern is no longer recognized accurately. In of the shape of pattern marked, resulting in a problem that considerable time and cost are required for generation of mask. Moreover, there rises a problem that management of mask is very complicated with increase in the number of masks generated.
In addition, the Japanese Patents Laid-Open Nos. HEI 2-187288 and 2-251387 disclose laser marking apparatuses utilizing masks (hereinafter referred to as liquid crystal mask) formed by a liquid crystal device. This apparatus utilizes a liquid crystal mask as the mask used in the mask transmitting type laser marking apparatus explained above. A desired pattern can be depicted on a liquid crystal mask by driving the liquid crystal mask using the predetermined data. As explained, the pattern depicted on the mask can be generated and stored in the flexible data format by utilizing the liquid crystal mask. Accordingly, mask generation cost and management cost thereof can be remarkably be saved.
However, the laser marking apparatus utilizing such liquid crystal mask requires a driving device for driving the liquid crystal mask. Therefore, the marking apparatus itself brings about increase in size and rise of cost. Moreover, since the liquid crystal panel is limited in its operation life and the liquid crystal panel must be replaced in every predetermined period, a running cost is necessarily raised. addition, since the marking line is processed deeply, when this method is employed for the marking at the surface of thinner electronic parts, such electronic parts are damaged with the laser beam used for irradiation. Therefore, the beam scanning type laser marking apparatus explained above cannot be used for marking the desired pattern on the thinner electronic part.
Furthermore, when a processing object is an electronic part, the pattern to be marked sometimes includes a wider pattern such as a trade mark. In the case of marking wider patterns on the electronic part with the conventional beam scanning type laser marking apparatus, it must be considered as a problem that the processing capability is lowered remarkably in comparison with the mask transmitting type marking apparatus.